Fuel surge with modded CAG carby

[Crash Dummy]

Hey guys.

I'm really in a pickle here. I'm going to Butterfly Farm tomorrow and my sleeper engined F2 is giving me trouble. It goes like stink but if you hold the throttle on wide open for 10 seconds or it just runs out of fuel. This is getting to be REALLY annoying as you might imagine and the F2 isn't an easy bike to work on so that makes it twice as annoying.

So here's what done.
I figured it must be draining the fuel bowl. That's a given because it goes like absolute stinky right up until it leans off. This isn't the only carb i've had this problem with either. What can I do ?
I've got a full tank of petrol. The fuel cap as enough ventilation. Oooh my it does. I've made sure the fuel nipple on the tank didn't have any gunk in it and drilled it out to 4.5mm just to be sure. The fuel tube is great with no kinks anywhere and it's a down hill run all the way to the carb. The fuel filter is good and seems to be clean and free flowing. I've removed the fuel tap and filled in the petcock with epoxy putty and drilled straight down the center of it so their is a straight path for the fuel to flow into the carburettor. The forks that rest on the float have been set to try get the fuel level as high as possible but i can't confirm exactly how high the fuel level is. The vent for the fuel bowl is functional and clear...

WTFBBQROFLCOPTER!!!!

Can anyone help me before I cry. Nobody wants to see a moderator cry.

[RONIN]

Hi Crash Dummy, although it mite not be the same problem, I recently have only just had my GRC sorted after the similar condition you describe happening.
What was found was that although the fuel filter appeared clean and flowed when off the carby it had water in it I could only go a few laps before I to thought the was a fuel starving problem. Every time it happened I to could slow down or if the motor cut out re start it and could once again go about 4 laps before the same happened again. As said this made me feel as though the fuel was flowing slowly and not keeping the carby bowl full. Also found the ignition lead was resting on the exhaust and had burnt through giving intermitent electrical problems. not sure if this is the same in your case, but understand only to well how frustrating this is for you.

[Matty_C]

hey CD have ya tryed the pumper ya got might work or maybe its a jeting prob or a nedle clip prob see if the clip has viabrated off of the lil notch happend to me to much playing arround with it made it to lose and it just cliked off and i couldent get the bike running properly. other then that i would chek reeds then and just give the engine a once over. thats all i can think of atm

[Crash Dummy]

Originally Posted by Matty_C

hey CD have ya tryed the pumper ya got might work or maybe its a jeting prob or a nedle clip prob see if the clip has viabrated off of the lil notch happend to me to much playing arround with it made it to lose and it just cliked off and i couldent get the bike running properly. other then that i would chek reeds then and just give the engine a once over. thats all i can think of atm

The pumper is on my other bike which has the full house 15:1 compression worked motor.
The carb is A-OK. I've had bits of it apart this arvo trying to get the low - mid mixture right. That's sweet as now as is the top. Just keeps running out of fuel..

I'm considering just pulling the fuel filter out completely for the moment. At least that will rule that out. There's no water in it i can confirm that.

I was actually thinking that perhaps the hole in the float level needle seat might be a bit too small and preventing fuel from making it's way into the bowl at any faster rate then a mere trickle.

Keep in mind the carb is ported to 14.6mm and this motor likes to suck some serious air so there's a LOT of fuel being used. I couldn't tell you what size jet is in it though because i'm using a tapered needle.

[Christo]

Try increasing your float level.

[ninja_zx.5r]

I was actually thinking that perhaps the hole in the float level needle seat might be a bit too small and preventing fuel from making it's way into the bowl at any faster rate then a mere trickle.

this "hole that ur talking about is called the seat if u have a spare carb u could try to drill out the seat on this carb and if it stuffs it swap but as far as i know ive never met any1 who had to do this
when u redrilled the petcock did u drill it wide enough?
cheers
Reece

[hudson44]

Yeah my stock carb was doing the same thing. Had good fuel flow, drilled out the tap etc and was still the same. Bent the float lever a little to increase the fuel in the bowl and its all sweet. Now i just have reed flutter at very high revs to fix.....

[Crash Dummy]

The hole i drilled in the petcock is i think 4mm or so. It's pretty big anyway. I'm in the process now of pulling the carb off the bike and getting it ready to do a bench test.. I'm going to give the carby a complete clean out and then i'll check the float level to see where it's at. If it's too low i'll set it higher. I'll have a think about drilling out the seat just a fraction if needed but i'm hoping it doesn't need it.

[mac90]

hehe i got a spare 17mm walbro that could help but im greedy want to put it on the blata rep engine i will get around to starting one day

then ill put my modded cag into the kids mini quad should be a good lil ride

unfortunatly i cant help but agree with running no filter strip the carby hit it with compressed air in every bit then set float level from scratch set mix pin in middle notch & try again lol

then grab a genuine filter for a rm or yz 80 you know they flow well

[Crash Dummy]

Okay time for the update

Fuel lines were good. The fuel filter was good. The fuel tap is quite restrictive. That's the BIG restriction. It's enough to concern me but I can't go without a tap so it'll have to stay in for now. I've stripped cleaned and reset my carby and found that everything was tip top.. kinda sorta..

I've reset the float level to be quite a bit higher and bent the float fork in such a way that now when the level drops it'll really let the bowl fill up QUICK. The float level is dead inline with the start of the cut out section for the float fork hinge bit.. LOL you'd know what i'm talking about... When the bowl is out and full of fuel with the float in the petrol.

All up I think it'll work now. Fingers crossed.

Another minor thing though. One of my experiments had messed up. My tapered needle main jet crapped itself because i'd drilled it too big. I went to tighten it up and sheered the thread off going into the atomization tube. End result. A angry face followed by a sigh and me reaching for the shelf-o-carburettors to fetch another then mod the jet to suit my tapered needle arrangement.
It's all good

Tomorrow is judgment day.